Here’s what Jun Okumura had to say on the issue, and I particularly like the incisiveness of his comments:
If her departure takes one awkward problem out of Mr. Abe’s hands, he can’t be pleased that Ms. Koike took the matter and its announcement into her own hands. This reinforces an image of a passive prime minister that does not take charge of the situation and instead allows the situation to dictate to him. In this respect, it does not help him that the two core personnel decisions he has made so far, creating a dual power structure of Cabinet ministers on one hand and the White House-style sub-Cabinet prime minister’s team on the other, and engineering the return of the Post Office privatization rebels, both backfired spectacularly. Another silver lining, of course, is that he will be able to replace her with a more conciliatory figure in dealing with counter-terrorism act whose extension will be the biggest and most urgent issue of the upcoming Diet session.